In recent years, a photographic printing paper capable of being quickly developed comprising a water resistant support consisting of a base paper having a polyolefin such as polyethylene and the like coated on both sides of the paper has been widely used.
Such supports for photographic printing paper, consisting of a base paper with a polyolefin layer coated on both sides thereof, may be divided into two groups: one is such that surface is glazed and the other is such that the surface is matted or provided with a pattern such as a silk web or the like. Of these, a support having no pattern at all and having a smooth, glossy surface is said to be better, and a support in which irregularities on both sides are moved as much as possible and which has a mirror-like smooth surface is particularly preferred.
In order to obtain such smooth supports, it has been proposed, for example, to use paper comprising a pulp having a fiber length of not more than 0.4 .mu.m and a void amount (pore diameter of 0.4 .mu.m or less) of at least 0.4 ml/g as the base paper constituting the support (JP-A-60-67940) (the term "JP-A" as used herein refers to an "unexamined published Japanese patent application"), to use a paper comprising a wood pulp having a mean fiber length of 0.4 to 0.9 mm, a mean fiber width of at least 13.5 .mu.m and a mean fiber thickness of not more than 4 .mu.m as the base paper (JP-A-60-69649), to use a paper comprising a mixture of natural pulp and 5 to 60 wt% of hydrophobic fibers (JP-A-61-275752), or to specify water removing conditions in obtaining a wet paper from a pulp slurry by the use of a two wire paper-making machine (JP-A-61-284762). In addition, an attempt has been made to increase the density of the base paper component to be used in the support for a photographic printing paper by calendering the base paper between metallic rolls and in this calendering, increasing the pressure, i.e., the pressure of the machine calender.
For coating with a polyolefin, e.g., polyethylene and the like, the extrusion coating method, i.e., the method of coating by extruding the polyolefin melted at an elevated temperature on the surface of the base paper, has generally been employed. In order to increase the smoothness of the support for a photographic printing paper, attempts such as increasing the thickness of the polyolefin coating layer and increasing the pressure applied at the time of polyolefin coating have been employed.
The above attempts in coating with polyolefin, however, are not sufficiently effective and are disadvantageous from an economic standpoint. The above methods to increase the density of the base paper have disadvantages in that problems with respect to appearance such as blacking and paper cockle readily occur. In summary, by any of the conventional methods, a support for photographic printing paper having sufficiently high smoothness has not been obtained.
A support for a photographic printing paper having sufficiently high smoothness cannot be obtained only by the above-proposed methods such as selecting a specific pulp as a component of the pulp slurry or specifying the dehydration conditions for obtaining a wet paper from the pulp slurry.